The blonde beauty said she would spend her time off concentrating on her writing before returning to The Biggest Loser at the end of the year.

"I'm just writing full-time and doing all my ninja stuff; I've got my Ninja business back in Melbourne," she said.

"So I'll probably be back for the next series at the end of the year, but I'm bowing out of the first four months."

A Channel Ten spokesperson said instead of replacing Hall with a fourth trainer, season eight would continue with the remaining three trainers: Michelle Bridges, Shannan Ponton and Steve "The Commando" Willis.